Examples of processes for retreading a tire are discussed in the present assignee's U.S. Pat. No. 5,007,978 issued to Presti and U.S. Pat. No. 5,098,268 issued to Robinson. Worn tread on a used tire casing is buffed off to a profile suitable for mounting a new tread. Then, a pre-cured and buffed tread is adhered about the periphery of the casing with a lamina of uncured cushion gum cemented between the tread and the casing. The tire is encased within curing envelopes and a vacuum is drawn through a valve in the curing envelopes for stretching the envelopes into intimate contact with all surfaces of the tread. The tire is then placed in an autoclave for several hours at an elevated temperature and pressure to cure the gum and positively bond the casing and tread together. The curing envelopes are removed and the retreaded tire is ready for use.
An important step in the above-described tire retreading process is the formation of a vacuum between the curing envelopes and the tire. The vacuum ensures that air or steam does not penetrate into the cushion gum during curing of the gum because the presence of air bubbles, or pockets of air, between the curing envelopes and the tire will prevent proper curing of the gum and will cause tread distortion. In addition, air pockets prevent pressure from being uniformly applied over the entire bonding area which also causes tread distortion.
To eliminate the formation of air pockets and to ensure the complete evacuation of air from between the curing envelopes and the tire, the present assignee has long suggested to its customers the placement of a wicking material between the curing envelopes and the tire. The recommended wicking material was a strip of multiple ply nylon.
U.S. Pat. No. 5,173,353 issued to Yamamoto also discloses placing a strip of nylon cloth between a curing envelope and tire for the purpose of venting air. See column 1, lines 14-16 and 27-30 of Yamamoto. In addition, Yamamoto discloses an air venting belt made of an expansible woven cloth such as rubber yarn. The end portions of the belt are laminated with a smooth film so that the end portions of the cloth which overlap the sidewall of the tire do not cause cloth-type imprints to be formed on the smooth sidewalls of the tire.
Another method of venting air between a curing envelope and a tire is disclosed in U.S. Pat. No. 5,306,130 issued to King et al. King provides the inside surface of the curing envelope with a plurality of air passageways.
Although various ones of the above-referenced retreading wicks or means to vent air between a curing envelope and a tire may be satisfactory for their intended purposes, there is a need for an improved re-usable retreading wick which is durable and inexpensive to manufacture in addition to preventing air pockets from forming between a curing envelope and a tire when a vacuum is drawn.